The tightening of threaded fasteners commonly requires that a torque load applied to a fastener be within a prescribed tolerance range. Increasingly expanding use of assembled components has resulted in an ever increasing number of applications requiring utmost care in setting a wide variety of fasteners within stringent torque tolerance limits. Such increased demand for precisely torqued jobs has also resulted in additional need for a reliable, simplified system for indicating peak applied torque loading of the fastener and, frequently, for a continuous reading of instantaneous torque being delivered to a job under running load conditions.
On fixtured air tools, it has been known to obtain torque signals from reaction torque transducers. In a fixture, an air tool is restrained from turning, in reaction to the fastener which is being brought up to torque, by a flange at the front of the air tool which is bolted to the fixture. A reaction torque transducer is a tubular section with a flange at each end mounted between the motor flange and the fixture with strain gages bonded to the tubular section. Wires lead from the strain gages to a junction box on the fixture where an external measuring device or signal conditioner may be plugged in. As the tool runs down a fastener, torque builds up in the fastener and reaction torque builds up on the transducer. The strain gages are displaced elastically, changing their resistance to current flow. This change in resistance is measured, amplified and scaled for recording or display in units of torque. Sometimes, fixtured tools with reaction torque transducers re audited, using a portable meter. Other times, fixtured tools with reaction torque transducers are permanently hooked up to electronic display and/or recording devices, monitoring torque on each job.
Reaction torque transducers on single hand-held portable tools present other problems. Weight and size become immediately significant. Wires and connections become vulnerable and easily damaged. Tools may become larger and bulkier and their maintenance may become complex. Under certain circumstances, an operator can affect the torque signal by twisting the air tool. E.g., in the angle nutsetter with a reaction torque transducer placed in a long axis of the tool before the angle gears, twisting of the tool handle adds or subtracts from the signal. Costly and frequently cumbersome solutions have been suggested to avoid operator influence and/or to internally isolate such torque reaction transducers from the tool handle, but such solutions heretofore have not proven to be viable.